The invention relates to systems for installing offshore equipment and supporting offshore operations. More specifically, embodiments of the present invention relate to configurable vessels for installing offshore equipment used in the exploration and production of hydrocarbons.
Offshore systems used in the exploration and production of oil and gas reservoirs are large complicated structures that require a number of specialized operations to be performed during the installation process. These installation operations involve precise positioning of heavy loads in an inherently unstable offshore environment that requires vessels to possess good hydrodynamic performance in order to safely and successfully perform the operations. Because, of the variety of installation operations that need to be performed and the high capital costs of the required vessels, installation companies typically consider the full range of possible jobs that can be performed and select large, general-purpose vessels.
These large, general-purpose vessels generally command high daily rental rates in order to cover the expenses involved in building and operating the vessels. Therefore, many owners prefer to keep the vessels in operation so that their utilization rate is as high as possible. Given the weather and sea-state sensitivities involved in offshore operations, there are often long periods of unplanned downtime, which, when combined with the high planned utilization rate, result in significant delays to projects that are currently being executed as well as all projects that are in backlog.
The capabilities of the installation vessel to be used on a project are very important for project planning because there are very few vessels that can do large deepwater projects. For example, any one market may only have one or two installation vessels at any time. Therefore, all large-scale projects must be designed around the capabilities of the vessels available. For example, in the design of an offshore production platform, the available installation vessel's capabilities will typically drive the structural design of the topsides deck, the systems used for maneuvering the hull, and the components of both the mooring and riser systems.
Although a large, general-purpose installation vessel can perform many common installation operations, some of these operations could alternatively be performed by other, more efficient vessels, reserving the large, general-purpose vessels for those functions that actually require the capabilities of the larger installation vessel. Building smaller, purpose-built installation vessels is also problematic as the utility of these vessels may be limited, making the economics difficult to justify.
One of the most important drivers for large projects is whether or not a topsides lift is needed. Lifting topsides often requires a very large derrick barge, which are limited in number and therefore may be difficult to schedule. Installation of the topsides using a float-over procedure eliminates the need for a topsides lift by transporting the topsides on a barge to a floating hull. The floating hull is partially sunk so that the topsides can be floated over the hull into position. One issue with using a float-over procedure is that the barges used to transport the topsides often have to be specially constructed for a particular project, making their use prohibitively expensive.
Thus, the embodiments of the present invention are directed embodiments of to a modular, configurable system that can support a variety of installation operations that seek to overcome these and other limitations of the prior art.